The unique apex filler applying apparatus to which the present invention is directed is an improvement over the apparatus disclosed in prior U.S. Pat. No. 5,100,497 which is owned, of record, by the Assignee of the present invention. The apparatus disclosed and claimed in said prior art patent operates quite effectively to apply apex fillers of limited aspect ratios--i.e.: for applying apex fillers having a radial dimension of up to approximately three-quarters (3/4) of an inch with a base width on the order of about one quarter (1/4) of an inch to constitute an aspect ratio on the order of approximately 3:1. The prior art apparatus, however, is incapable of applying apex fillers of any significantly greater aspect ratio than the aforementioned 3:1 ratio without causing the undesirable scalloping, curling or cupping of the apex filler in the completed tire bead sub-assembly.
As will become apparent, the aspect ratio desired for current apex fillers adapted for use in low profile tires will likely fall within the range of from about eight to one (8:1) to as much as sixteen to one (16:1). The prior art mechanisms for creating combined bead ring and apex filler assemblies--as exemplified by the apparatus disclosed in U.S. Pat. No. 5,100,497--simply can not create such assemblies with an apex filler having aspect ratios of such increased magnitude. To better understand the configuration of apex fillers having aspect ratios of relatively higher magnitude, a typical apex filler having about a three and one-third (31/3) inch radial dimension and a base width of on the order of one quarter (1/4) inch constitutes an aspect ratio of on the order of approximately thirteen to one (3:1). With the width of the apex filler falling in the range of from a little less than to a little more than approximately one quarter (1/4) inch and with the radial dimensions of the apex filler falling within the range of from about three (3) inches to as much as about five (5) inches, the aspect ratios are considerably more significant than are encountered with prior art configurations.
In order more clearly to comprehend the historic, and current, function of apex fillers it should be understood that a tire has two, laterally spaced bead portions which define the innermost diameter thereof. Each bead portion incorporates an annular, metallic, bead ring assembly which provides hoop strength and structural integrity to the bead--i.e.: the rim-engaging structure of the tire. Normally, each tire bead sub-assembly also includes an apex filler in addition to the metallic bead ring, because the combination assures a smooth transitional juncture between each bead portion and the adjacent sidewall portion of the tire.
While low profile tires are deemed to enhance the aesthetic appearance of the vehicle on which they are mounted, operation of a vehicle having low profile tires at high speeds may reduce the lateral stability of the vehicle. Specifically, if the design of the low profile tire incorporates a reduction in the rubberized material forming the sidewall of the tire, cornering the vehicle at high speeds is adversely affected by the minimization of the rubberized material in the sidewall. The application of additional plies within at least the side wall will enhance the lateral stability of the tire, not only at excessive cost but also by providing an unnecessary addition to the thickness of the tire beneath the tread portion.
The lateral stability of the tire sidewall has been found to have been satisfactorily increased to permit operation at high speeds merely by extending the apex filler further into, and in some situations to about the shoulder of, the tire sidewall. However, current vehicular tire design utilizes the apex filler to do more than provide for a smooth transitional juncture between each bead portion and the adjacent sidewall of the tire. In addition, apex fillers are currently employed as performance-tuning members. That is, they serve to increase cornering stability and to dampen harmonics inherent in the vehicular undercarriage on which the tires are mounted. Although this is a relatively easy fix for the tire designer, current apparatus for applying an apex filler of the desired size to the bead ring simply won't produce an acceptable combination of bead ring and apex filler--i.e.: a tire bead sub-assembly.
To facilitate the manufacture of the tire, the annular bead ring and the apex filler are generally provided as a composite tire bead sub-assembly about which the plies of the tire may be wrapped. The aforesaid U.S. Pat. No. 5,100,497 significantly advanced the technology of applying an apex filler to an annular bead ring.
The advancement achieved by U.S. Pat. No. 5,100,497 is best understood by recognizing the two primary manufacturing techniques that antedated that patent. One such historic prior art method of fabricating the tire bead sub-assembly applied a flat strip of elastomeric material along the inner circumference of a rubber-coated, annular, bead ring and then encapsulated the bead ring by wrapping the strip radially outwardly about the bead ring. That portion of the strip which extended radially outwardly from the bead ring constituted the apex filler. This method was fraught with difficulties, particularly in splicing the abutting ends of the wrapped strip. When the elastomeric strip was so wrapped to encapsulate the bead ring, the outer circumference of the material had to be stretched to accommodate the difference between the circumferential dimension of the bead ring and the circumferential dimension at the radially outer periphery of the elastomeric strip. This stretching induced stresses which produced warpage in the form of dishing, cupping or scalloping along the radially outer portion of the resulting apex filler. This warpage was not constant from filler to filler, and it therefore increased the difficulty of maintaining quality control between successive tires employing bead assemblies made by this method.
Another historic method of manufacturing a tire bead sub-assembly applied an apex filler strip to a rotating bead ring until the starting point of the apex filler strip was adjacent the point at which the apex filler strip was first applied to the bead ring--approximately one revolution--at which time the apex filler strip was severed. The partially combined bead ring and apex filler assembly was then moved to a second processing station where a gripping and stretching apparatus engaged the apex filler to close the ends and complete the tire bead sub-assembly. This also resulted in stretching the radially outer circumference of the apex filler strip more than that portion of the filler strip which had been joined with the bead ring. This stretching causes the same distortion problems inherent to, and as described in conjunction with, the previously discussed prior art methods.